During the differentiation of macroconidia by Neurospora, NADase activity appears and increases to its maximum specific activity in completed conidia. This activity is almost entirely extra-cellular and is rapidly destroyed during the early stages of germination. These results have led four independent workers to suggest essential roles for NADase in either the differentiation or germination of conidia. The entire process of synthesis, shipment out of the cell and destruction of the enzyme constitutes and interesting example of post-translational control enzyme activity. Structural mutants of NADase will be isolated because their phenotype should reveal decisively the function of NADase in Neurospora. NAD will serve as a source of nicotinamide which may permit me to select mutants unable to grow on NAD using inositol-less death selection. If the high solubility of NADase and the low requirement for nicotinamide frustrate selection, two-non-selective methods are available: (1) mutants will not destroy NAD ion so that NAD can be detected by reduction of a tetrazolium dye; (2) nicotinamide can be detected by reaction with cyanogen bromide and anilin whereas NAD does not react. I will purify the enzyme, determine its molecular size and structure and develop immunologic methods for detecting it. These studies are necessary to confirm the structural nature of mutants. In addition it has been proposed that enzyme localization in the cell wall and extracellular compartment depends on size and subunit structure.